1. Field of the Invention
The present invention is directed to a procedure which combines asthma analysis and therapy in the context of magnetic resonance scanning of a subject.
2. Description of the Prior Art
Asthma is a serious illness of the lungs characterized by recurring attacks of dyspnea (shortness of breath), a feeling of pressure on the chest, wheezing, cough, fear, etc. The distressing symptoms are caused by a constriction of the bronchial tubes, which are the tube-like structures that carry air to and from the lungs. The length of an asthma attack can vary; it may last for a few minutes or several hours, or longer.
The primary cause of so-called xe2x80x9ctruexe2x80x9d asthma is sensitivity to certain substances, generically referred to as allergens.
There are approximately 100 million asthmatics worldwide. Asthma is one of the most common causes of death of persons under 50 years of age in highly developed countries, wherein instances of this illness continuously increase. Although several types of medication are available for asthma therapy, each type of medication is effective only for specific groups of patients. Other than the triggering effect of an allergen, the mechanism which produces an asthma attack is still not completely understood, particularly on an individual patient basis. Because of this lack of knowledge, it is extremely difficult, if not impossible, to find an optimal dosage for the medication. The patient himself or herself is not aware of the presence of the latent illness before a dangerous condition already has been reached, typically the occurrence of an attack. Under normal circumstances, an asthmatic feels comfortable during times when the illness is latent, but begins to experience repeated and surprising asthma attacks, which can be very dangerous. The separation in time, and the seeming spontaneity, of such asthma attacks compound the problem of prescribing an appropriate dosage of therapeutic medication.
The following examination techniques and dosage prescriptions are currently practiced in the field of asthma therapy.
A thorax X-ray is a fast and inexpensive examination technique, but has a highly limited informational content, because the thorax X-ray image only represents a two-dimensional projection of the lung onto the X-ray film, and shows very little soft tissue contrast.
Computed tomography is a relatively expensive method and requires longer measuring time and exposes the patient to a dose of ionizing radiation. Computed tomography is therefore not practical for patients requiring repeated examinations, particularly young patients.
Lung function measurements, such as those obtained by connecting a patient to a ventilator, are relatively inexpensive and allow conclusions to be made regarding the functioning of a patient""s lungs with a specific time resolution. Such lung function measurements, however, provide no visual information of the lungs themselves.
As a supplement to lung function measurements, an allergen provoker can be administered to the patient so that changes in the functioning of the patient""s lungs as a result of the presence of the allergen can be monitored and analyzed.
Scintigraphy (i.e., imaging using a scintillation camera) provides spatially resolved functional information, but the spatial resolution is relatively modest and can be conducted only by personnel trained in nuclear medicine.
The production and properties of hyperpolarized gases are well known and are described, for example, in PCT Application WO 99/08766. Obtaining magnetic resonance images after administering a hyperpolarized gas to a patient is a known technique for monitoring physiological processes because the hyperpolarized gas produces a uniquely identifiable magnetic resonance (MR) signal, and thus the diffusion of the hyperpolarized gas into body tissue and organs can be monitored in one or more MR images. The use of this technique for lung imaging and analysis is described in the article xe2x80x9cKernspintomographie der Lunge mit hochpolarisiertem Helium-3,xe2x80x9d Schreiber et al., Physilkalische Blxc3xa4tter 55, No. 3 (1999) pages 45-47. 3He or 129Xe is polarized up to approximately 60 percent by spin exchange under laser irradiation. This hyperpolarized gas (HPG) is administered to the patient for one breath. During the inhalation and the subsequent phase wherein the air is held, a series of MR images of the patient is obtained. The measuring time is determined by the subsidence of the hyperpolarization in the lung, and by the time that the patient holds his or her breath. The hyperpolarization subsides primarily due to reaction with O2 (see xe2x80x9cPhysics of Hyperpolarized Gas NMR in Biomedicine,xe2x80x9d Darrasse, European Radiology 9, Abstracts B2 (1999)) and the flip angle of the MR sequence (see xe2x80x9cDynamically Adaptive Hyperpolarized Noble Gas MR Imaging Using Spatially Selective RF Pulse Encoding,xe2x80x9d Zhao et al., European Radiology 9, Abstracts B3 (1999)).
Only the polarized noble gas is visible in the MR images, thereby providing information regarding ventilation of the lung with a high degree of spatial resolution. The results of different MR measuring sequences are described in the article xe2x80x9cLung Air Spaces:MR Imaging Evaluation With Hyperpolarized 3He Gas,xe2x80x9d de Lange et al., Radiology, Volume 210, No. 3, pages 851-857 (March 1999). Depending on the measuring sequence, one or several images of the ventilated areas of the lung, in one or several slices can be acquired. Alternatively, a time history of the ventilation can be acquired, but with a relatively low spatial resolution, as described in xe2x80x9cUltrafast MR Imaging of Lung Ventilation Using Hyperpolarized Helium-3,xe2x80x9d Schreiber et al., European Radiology 9, Abstracts B28 (1999).
Subsequently, breathing air, possibly enriched with oxygen, is administered to the patient and after a waiting period, when it is assured that the patient""s blood oxygenation is normal, the examination can be repeated or the patient can be discharged.
It is an object of the present invention to provide a combined procedure for asthma analysis and therapy determination which does not expose a patient to ionizing radiation and which provides high time resolution and spatial resolution.
The above object is achieved in accordance with the principles of the present invention and integrated asthma analysis and therapy determination method wherein hyperpolarized gas is administered to a patient in a xe2x80x9cnormalxe2x80x9d state, i.e. the patient is not exhibiting acute asthmatic symptoms, and an MR scan of the patient""s lungs is undertaken, to obtain a first MR image or a first MR image sequence. Subsequently, an allergen provoker is administered to the patient, hyperpolarized gas is again administered to the patient, and a further MR scan of the patient""s lungs is conducted, so as to obtain a second MR image or a second series of MR images. Subsequently, asthma therapeutics, such as medication, are administered to the subject, hyperpolarized gas is again administered to the subject, and another MR scan of the patient""s lungs is conducted, to obtain a third MR image or a third series of MR images. The patient then leaves the MR system. The first, second and third images or the first, second and third series of images are then compared with each other so as to obtain an indication of the difference between the state of a patient""s lungs in the xe2x80x9cnormalxe2x80x9d condition and in the condition after allergen provocation, and in the condition after asthma therapy has been administered. The physiological affect of the presence of the allergen can be ascertained by comparing the first and second images, or first and second series of images, and the effectiveness of the administered asthma therapy can be ascertained not only by comparing the second and third images, or second and third series of images, but also by comparing the first and third images, or the first and third series of images.
After each MR scan, the patient""s blood oxygenation can be measured and/or an electrocardiogram (ECG) can be obtained from the patient, in order to insure that the patient is not adversely affected by the procedure. Such a blood oxygenation measurement and/or an ECG also can be obtained prior to conducting the first MR scan, in order to provide baseline data.